The invention deals with a direct current controlled trigger or control circuit for triacs connected via a consumer circuit to a source of alternating current supply voltage.
For power control of consumers of alternating current networks, triacs are used in increasing numbers. Traics provide in the simplest manner the full wave operation of the consumer with the phase cut off, since only a single control power element is required. At a predetermined angle of each half wave the triac must therefore be ignited.
A great number of circuits which produce ignition pulses suitable for ignition of triacs are known and require a different amount of structural elements. An arrangement for phase cut off control is disclosed in the DE-OS No. 24 03 097. With the known control circuit the current for loading a load capacitor is adjustable such that--in dependence upon the direct control current voltage--the resistance of the drain-source-channel (r.sub.DS) of a field effect transistor is changeable. For coupling the half waves, two resistors are used in a bridge circuit with the field effect transistor, and serve for the symmetrization of the current flow angle of the positive and negative half waves.
A disadvantage of the known control circuits is the fact that relatively many structural elements are required which on the one hand increase the expenses and the space requirements and on the other hand increase the reliability risks.